Tarnish resistant silver based dental casting alloy capable of bonding to porcelain

ABSTRACT

An alloy composition comprising about 35-60% Pd, at least about 0.5-7% of one member of the group consisting of Cr, Fe, In and Sn and from about 0 to 5% of the group consisting of Si, Ni, Co, Ta, and Ti, and the rest Ag, has been found useful in the dental arts where a porcelain is required to be fused directly to the alloy.

United States Patent In ersoll Dec. 30 1975 [54] TARNISH RESISTANT SILVER BASED 2,070,271 2/1937 Gwyn 75/173 R X DENTAL CASTING ALLOY CAPABLE OF 2,222,544 11/1940 Spanner BONDING TO PORCELAIN 3,155,467 11/1964 Yamamoto et al. 75/173 R X [75] Inventor: Clyde E. Ingersoll, Tonawanda, FOREIGN PATENTS OR APPLICATIONS N Y 628,572 4/1936 Germany 1. 75/173 R [73] Assignee: Williams Gold Refining Company Primary Exammer-L Dewayne Rutledge Incorporated Buffalo Assistant ExaminerE. L. Weise [22] Filed: Aug. 5, 1974 Attorney, Agent, or Firm-Christel & Bean [21] Appl. No.: 494,566

[57] ABSTRACT [52] us 75/l72 75/173 R An alloy composition comprising about 35-60% Pd, at

[51] 5/04, 6 5/06 least about 0.5-7% of one member of the group con- [58] Field of n 75/l373R 172 G sisting of Cr, Fe, In and Sn and from about 0 to 5% of the group consisting of 'Si, Ni, Co, Ta, and Ti, and the [56] References Cited rest Ag, has been found useful in the dental arts where a porcelain is required to be fused directly to the al- UNITED STATES PATENTS l,229,037 6/1917 Cooper 75/173 R 1,999,866 4 1935 Capillon et al. 75 172 0 7 ClaImS, N0 Drawings TARNISH RESISTANTSILVER BASED DENTAL CASTING ALLOY CAPABLE 'OF BONDING TO PORCELAIN 1 I BAC oRoUNDoF THEjINVENTION 1. Field of the invention This invention relates to silver -palladium alloys employed in the dental and jewelry arts which are resistant to tarnishing; have superior ductility and work hardening characteristics and have a coefficient .of thermal expansion close to that of porcelain, and can form an oxide coating so that the alloy may be fire bonded to porcelain.

2. Description of the Prior Art The American Dental Association (ADA) has had Specification 5 for many years, which included four types-of casting alloys in common use in dentristry. Type IV, of greater significance here, relates to alloys for having a 150' minimum Vickers hardness and hardneable'to 220 minimum Vickers hardness, whi ch are for use inpartial dentures, bars, clasps, and unit castings. In addition to the four types, ADA has a proposed specification for alloys having high melting temperature and high yield strength (similar to Type IV), and a coeff cient of thermal expansion close to that of the porcelain to be fired to it and which forms an oxide coating for bonding to the porcelain.

SUMMARY OF THE INVENTION The present invention comprises alloys of silver and palladium containing at least one member of the class consisting of Cr, Fe, In and Sn and optionally containing one or more members of the class consisting of Si, Ni, Co, Ta, and Ti. Such alloys have good tarnish resistance, ductility and work hardening characteristics, have coefficients of thermal expansion close to that of procelain, and can be directly bonded thereto and have Vickers hardness values of from 150 to above 220.

OBJECTS OF THE INVENTION It is an object of this invention to provide a silver based alloy for bonding directly to porcelain.

It is a further object of the invention to provide a silver based alloy having the requisite properties of ductility, hardness, work hardening, tarnish resistance and coefficient of thermal expansion for use in the dental arts for bonding directly to porcelain, together with the properties necessary for casting, such as fluidity for filling a mold completely and for polishing.

Further objects of the invention will become apparent from the following description and claims.

DESCRIPTION OF THE INVENTION A dental alloy meeting the requirements of the ADA proposed specification set forth above should have in addition to the hardness requirements, good tarnish resistance and good work hardening characteristics.

Ductility is a highly desirable property in dental alloys since, in many instances, the dentist must burnish the dental piece for better adaptation. Brittle margins are likely to break off during such burnishing operations.

Good work hardening characteristics are important for easier manipulation by the dentist or technician. Dental alloys are usually supplied in the form of wrought pieces. If the alloyworki-hardens' rapidly, only a small amount of reduction can be achieved after each strain relief treatment.

TARNISH RESISTANCE,

Publication No. 31,008 of the Department of Commerce (dated Sept. 23, 1927') gives theres'tilts of tests on the tarnishability of silver-based alloys. In thepublication, the alloys were exposed to sodium polysulfide for a period of eight minutes and the discolorations noted. In the present case, this'test was modified by employed, cast bar specimens were prepared by first grinding and polishing by normal metallurgical methods followed by sandblasting the surface to be exposed to ammonium sulfide for eight minutes.

A numerical scale was established by exposing pure silver bars to ammonium sulfide for times ranging from 0 to l45 seconds, giving a scale of 0 for no exposure to 10, almost black. In making the test, a portionof the test bar was covered so that the exposed portion and unexposed portion could be directly compared. Dental amalgam rated 9 on this scale, an alloy'of silver-25 palladium rated 5. An -ADA certified gold alloy rated between 0 and l and was assigned i. To be acceptable for dental work of the type covered in ADA'Specification 5,-and the proposed specification the tarnish rating should be no higher than about 5.5.

HARDNESS Since the hardness is not translatable from one alloy system to another, some other mechanical property must be employed to compare different systems. In the present case, the 0.1% offset yield strength was used as the comparable property. The Vickers hardness shown in the table is for a silver base alloy of this invention having the same 0.l% offset yield strength as the ADA Specification 5 Type alloy.

TABLE I These Values are all in the as cast" condition.

While copper has been employed as a hardening agent for silver-palladium alloys (see U.S. Pat. No. 2,198,400), too high a concentration of copper is known to cause brittleness (see U.S. Pat. No. 2,259,668). As shown in copending case Ser. No. 494,5 65, a number of elements may be added to silverpalladium alloys to increase the Vicker hardness numbers. It has been found that in order to meet the requirements of proposed ADA Specification and to have suitable tarnishing resistance and cold reduction properties, the additional alloying elements should be at least the member from the group selected from the class of Cr, Fe, In and Sn and, optionally, one or more members of the group selected from Si, Ni, Co, Ta and Ti. The alloys of this invention comprise about 28-64% Ag, about 34-60% Pd, about 0.57% of at least one member of the class consisting of Cr, Fe, In or Sn and 3 to about of Si, Ni, Co, Ta or Ti.

THERMAL EXPANSION Because of the high coefficients of thermal expansion imparted by In and Sn, the amounts of these elements which may be employed in the alloys of the invention is less than the upper limit of in the alloys of my copending application, Ser. No. 494,565. Zn is unusable as an additive in the present case because of its high vapor pressure at porcelain firing temperatures.

The following table gives a number of examples of alloys exemplary of the present invention.

4 taining Fe further containing a member selected from the group consisting of about 0.5% Ta, about 2.0% Ni, and about 0.5% In and about 0.5% Sn.

2. The alloy of claim 1 wherein the composition is about 37.5% Pd, about 0.5% In, about 0.5% Sn, about 1% Ti and the balance Ag.

3. The alloy of claim 1 consisting essentially of about 48% Pd, about 5% Fe, about 0.5% in, about 0.5% Sn, and the balance Ag.

4. The alloy of claim 1 consisting essentially of about 46.5% Pd, about 2% Fe, about 2% Ni and the balance Ag.

EXAMPLE (ELEMENTS GIVEN 1N A110 Cold No. Ag Pd Cr Fe 1n Sn Other HV Tarnish Reduction 1 Hal 57.7 1 6 Si 0.7 215 3 68% 2 Hal 50.4 1 1 Ni 5.0 216 4 62% 3 Ba] 45 2 Co 2.0 217 4 80% 4 Bal 45.9 4 Ta 0.5 212 4 89% 5 Bal 46.5 2 Ni 2.0 212 2 90% 6 Ba] 48 5 0.5 0.5 221 3 86% 7 Bal 37.5 5 0.5 0.5 T1 1.0 210 3 81% What is claimed is: 5. The alloy of claim 1 consisting essentially of about 45.9% Pd, about 4% Fe, about 0.5% Ta and the balance Ag.

6. The alloy of claim 1 consisting essentially of about 45% Pd, about 2% Cr, about 2% Co and the balance Ag.

7. The alloy of claim 1 consisting essentially of about 57.7% Pd, about 1% In, about 1% Sn, about 5% Ni, and the balance Ag. 

1. AN ALLOY CONSISTING ESSENTIALLY OF ABOUT 28-64% AG, ABOUT 37.5-57.7% PD, ABOUT 0.5-7% OF AT LEAST ONE MEMBER OF THE CLASS CONSISTING OF CR, FE. IN AN SN AND FROM 0 TO ABOUT 5% OF A MEMBER OF THE CLASS CONSISTING OF SI, NI, CO, TA, TI, ALL TOTALLING 100%; SAID ALLOY HAVING A VICKERS HARDNESS OF 150-220; SAID ALLOY WHEN CONTAINING SN FURTHER CONTAINING A MEMBER SELECTED FROM THE GROUP CONSISTING OF ABOUT 0.5% IN, 1.0% TI, 5.0% NI, 17% SI, AND 5% FE; AND SAID ALLOY WHEN CONTAINING FE FURTHER CONTAINING A MEMBER SELECTED FROM THE GROUP CONSISTING OF ABOUT 0.5% TA, ABOUT 2.0% NI, AND ABOUT 0.5% IN AND ABOUT 0.5% SN.
 2. The alloy of claim 1 wherein the composition is about 37.5% Pd, about 0.5% In, about 0.5% Sn, about 1% Ti and the balance Ag.
 3. The alloy of claim 1 consisting essentially of about 48% Pd, about 5% Fe, about 0.5% In, about 0.5% Sn, and the balance Ag.
 4. The alloy of claim 1 consisting essentially of about 46.5% Pd, about 2% Fe, about 2% Ni and the balance Ag.
 5. The alloy of claim 1 consisting essentially of about 45.9% Pd, about 4% Fe, about 0.5% Ta and the balance Ag.
 6. The alloy of claim 1 consisting essentially of about 45% Pd, about 2% Cr, about 2% Co and the balance Ag.
 7. The alloy of claim 1 consisting essentially of about 57.7% Pd, about 1% In, about 1% Sn, about 5% Ni, and the balance Ag. 